In intensive medicine, and also in many operating procedures, it is often necessary to introduce catheters into the large veins of the body to apply liquids and, for example, heart stimulating medication. Catheters are also introduced into the arterial vessel system, for example to the radial artery in the hand or the femoral artery in the groin to measure the blood pressure directly and to take blood to determine the amount of gas in the arterial oxygenated blood. Both arterial and venous catheter localisations are standard procedures not only in surgical clinics. Penetration of large vessels is also performed on numerous occasions in diagnostic procedures, for example special catheter examinations in angiography.
In particular the penetration of the subclavian vein beneath the collarbone and the penetration of the internal jugular vein on both sides of the neck is accompanied by a wide variety of complications, which are mainly caused by failed and repeated attempts at penetration. This can lead to so-called pneumothorax, injuries to the neck artery, haematoma formation and other serious iatrogenic injuries. When penetrating the radial artery or the femoral artery injuries to the vessels by multiple blind penetrations are possible even extending to an occlusion of the vessel concerned. Furthermore frustrated attempts at penetration lead to loss of time, which is most undesirable, for example, in the case of an emergency and even when preparing for an elective operation.
In order to avoid iatrogenic injuries when penetrating large veins it is known to determine the position and the course of the vessel to be penetrated sonographically. For example the image producing sonograph is used to localise the internal jugular vein of the neck. A great disadvantage of this practical method of avoiding iatrogenic injuries when penetrating large veins is, however, the outlay in apparatus. This has led to this simple and elegant method not being widely used, despite the extensive distribution of image producing sonographic devices.
To avoid difficulties when localising the vessel and to reduce the risk of complications it is also known to determine the position and the course of the vessel to be penetrated by means of ultrasonic Doppler sonography. This is done by means of a probe whose sonic head is aligned with the vessel to be penetrated and of an external receiver connected mechanically to a regular syringe. The receiver is arranged in the extension of the needle axis parallel to the housing of the syringe which is connected to the needle by way of a separate material line. The ultrasonic transmitter usually operates at a frequency of 4 to 8 MHz.
The ultrasonic waves are reflected by the blood corpuscles moving in the vessel and are thereby distorted due to the Doppler effect. The receiver receives the reflected ultrasonic waves and transmits via a loudspeaker a characteristic sound, which in the case of arteries is a pulse-synchronised hissing and in the case of veins is a respiration-dependent howling. Since the noise increases when approaching the vessel that is being sought ultrasonic Doppler sonography provides a simple means of localising vessels to determine the direction of the blood flow, since in the case of blood flowing towards the transmitter the ultrasonic waves are reflected at a higher frequency, and at a lower frequency in the case of blood flowing away from the transmitter.
There are however problems in manipulation since on the one hand the probe must be positioned, and independently thereof the needle of the syringe connected to the receiver must be introduced into the tissue. This usually requires an assistant to hold and position the probe, or at least occupies both hands of the examiner. Furthermore, the syringe connected to the receiver is a relatively complicated and scarcely compact special model which, as a result of its bulk and unfavourable centre of gravity can only be manipulated with difficulty. Emergency treatment is therefore not possible with syringes of this kind.
A further disadvantage common to both methods is that apart from the actual syringe the probe and--in Doppler sonography--the receiver have to be sterilised or be sterile-packed, which is not only troublesome but may also lead to damage to the electrical components.